In a synchronous motor the starter is provided with windings to carry a rotating alternating field and the rotor includes a field winding energized by a direct current source. During normal operation, the rotor is rotating at a speed corresponding to the rotational speed of the field created within the stator windings. Such a synchronous motor should operate with the rotor rotating at the same speed as the rotating field of the stator, i.e. zero slip or locked; therefore, during start up the rotor has to be accelerated from rest or some subsynchronous speed to the speed of the rotating field of the stator. For this reason, it is somewhat common practice to start a synchronous motor by converting to an induction mode of operation. To do this, a field winding of the rotor is provided with a discharge resistance circuit. By removing the D.C. excitation to the field winding and using the discharge circuit for induced current flow, the field winding is connected in accordance with an induction mode. In this mode of operation, a high starting torque can be created and a torque to force the motor into synchronization is possible. Various control arrangements have been used for shifting from the synchronous mode with the field winding excited by a D.C. source and an induction mode with the field winding provided with a discharge circuit. These prior attempts have been quite complex and somewhat difficult to predict and control. It is necessary to shift from the induction mode to the synchronous mode when the motor is experiencing a relatively low slip between the rotating field of the stator and the rotational movement of the rotor. This generally involves two separate circuits, one for measuring, in some manner, the low slip condition and one for measuring, in some manner, the zero slip condition. These two separate circuits must be coordinated to assure that when the motor is slipping, the induction mode is applied. In addition, when there is a zero slip condition due to a reluctance torque, the motor must be locked into the synchronous mode of operation with D.C. current in the field and maintained therein.